Effect on cardiac myosin of diverse methods of preparation

Separation of muscle proteins

This review covers various methods used in the separation and isolation of individual muscle contractile proteins. It is shown which methods have been most useful for the separation of contractile proteins and their fragments and in extending our knowledge of muscle biochemistry and physiology.

Heart contractile proteins

That several proteins of the sarcomere differ from one muscle to the next is well documented, and it is becoming evident that homogeneous muscles, like the heart, are also species specific. 1) Clear-cut evidence is available concerning myosin, and, to date, several types of molecules have been described. a) The myosins of white skeletal, heart, and smooth muscle differ in the activity of their Ca2+ and K+ATPases, as also in the structure of their light subunits. b) The Ca2+ATPases of the various cardiac myosins have been shown to exhibit species differences and correlate with the speed of shortening of the muscle. 2) The structures of tropomyosin, some troponin components, and alpha actinin (but not actin) appear to be unlike in the different types of muscle. 3) These phylogenic modifications may be related to the changes characteristic of the particular muscles under pathological conditions, which are accompanied by substantial increase in protein synthesis.

Force-generating capacity and contractile protein content of arterial smooth muscle

After correction for extracellular space (40%) determined from electron micrographs, the maximum isometric force developed by strips prepared from the media of the hog carotid artery (2.2 x 10(6) dyn/cm(2)) can be extrapolated to give a value of 3.7 x 10(6) dyn/cm(2) for the smooth muscle component of the strip. Three independent estimates of the myosin content of the smooth muscle cells were made based on (a) exhaustive extraction and purification with estimates of preparative losses, (b) the myosin catalyzed ATPase activity of media homogenates, and (c) quantitative densitometry of the peaks containing myosin, actin, and tropomyosin after disk electrophoresis of sodium dodecyl sulfate-treated media homogenates. The results were consistent and gave a myosin content of 5-10 mg/g media, or 8-17 mg/g cell. Method (c) gave myosin:actin:tropomyosin weight ratios of 1:3.2:0.8. Although measured force developed by the smooth muscle cell exceeds that of mammalian striated muscle, the myosin content in smooth muscle is about five times lower. The actin content of smooth muscle is relatively high. The actin and myosin contents are consistent with thick and thin filament ratios observed in electron micrographs of vascular smooth muscle.

Cardiac impairment in adrenal insufficiency in the cat. Reduced adenosinetriphosphatase activity of myocardial contractile proteins

Cardiac contractile protein ATPase activity was studied in cats 10 days after adrenalectomy at a time when the mean arterial blood pressure was 27% lower than that of control cats. The Ca 2+ -dependent, azide-insensitive ATPase activity of myofibrils isolated from the ventricles of adrenalectomized cats was 63% of the activity of control preparations ( P <0.025). Similarly, the specific activities of cardiac actomyosin (myosin B) and myosin from adrenalectomized cats had decreased to 54 and 75% of control values, respectively ( P <0.005). The percent reductions in ATPase activities in the three protein preparations from adrenalectomized animals were not significantly different, suggesting that the depression was associated with myosin per se. The reduction in the myosin ATPase activity in adrenal insufficiency was prevented by dexamethasone treatment adequate to prevent the decline in mean arterial blood pressure of the adrenalectomized cats. The reduction in cardiac performance in frank adrenal insufficiency may reflect a decrease in the rate of conversion of chemical to mechanical energy by the myocardial contractile proteins.